This invention relates to a prosthetic knee joint mechanism which includes a load-activated knee-stabilising device for restricting joint flexion.
It has long been known to include a stabilised knee as part of a prosthetic leg to achieve a natural looking gait, that is for the knee joint to resist flexion when under the load of part or all of the amputee's weight. Mechanical friction devices and hydraulic devices have been developed. In a known hydraulic stabilised knee joint mechanism, disclosed in Canadian Patent No. 2,134,999, resistance to flexion during the stance phase of the walking cycle and to extension during the swing phase is provided by restricting the movement of fluid between opposite sides of a rotary piston in a chamber filled with hydraulic fluid. In this mechanism the knee is locked by closing a fluid line by a valve interconnecting chamber parts on opposite sides of the piston using a valve member which moves when the application of the amputee's weight causes two resiliently connected parts of the mechanism to move relative to each other. The movement required to close the valve so to lock the knee is significant and creates a period of instability until the knee is locked. Also, overloading may damage the valve arrangement as it is directly operated.